Facebook users warned to check their privacy settings because of new search feature

Facebook users have been warned to check their privacy settings after the social network introduced a new search feature that added nearly two trillion old posts to its archive.

Until now, the search feature on the site focused mainly on groups, events and profile pages, with individual posts difficult to locate this way. However the update will see posts made publicly - as well as entire conversations - visible to anyone on the site via search.

Now, the site has indexed more than 2trn posts, and the search function enables users to seek out a specific post from any public profile, whether or not the two are friends on the site.

Facebook's vice president of search Tom Stocky announced the update in blog post; "When you search, you'll now see the most recent, relevant public posts along with posts from your friends," he said.

"Search results are organised to help you cut through the noise and quickly understand what the world is saying about a topic in the moment. You also can pull-to-refresh and see the latest public posts."

But the new feature, which has been added to make Facebook more accessible during major live events and to compete with Twitter, has been met with concern that older posts users would prefer did not appear again, could now be located.

Mr Stocky added: "Your search results are personalised and unique to you and, as always, you can only see things that have been shared with you. Likewise, you control who can see your posts on Facebook and it's easy to change the audience of your past posts any time."

However, privacy group Big Brother Watch says the lack of an announcement of the site is unfair on users.

The group's chief executive Renate Samson said: "Once again Facebook have rolled out changes with no clear mention of it on the site.

"Whilst the aim of this change may be to bring Facebook in line with services such as Twitter, users of Facebook may not wish for past posts to be made so public."

Ms Samson added that changing the privacy settings on old posts was more complicated than Facebook suggested.

"The process of hiding your old comments, known as "limiting past posts", is embedded deep in the privacy settings which few users explore unless otherwise directed to do so. This failure to alert users to the change or to the options to restrict their historical posts is disappointing," she said.